High film build coating composition containing polytrimethylene ether diol

ABSTRACT

The present disclosure is directed to a coating composition that is capable of producing coatings being sag-free at high coating thicknesses, having excellent adhesion to substrates, and good appearance. This disclosure is further directed to a coating composition comprising components derived from renewable resources.

FIELD OF DISCLOSURE

The present disclosure is directed to a coating composition that iscapable of producing coatings being sag-free at high coatingthicknesses, having excellent adhesion to substrates, and goodappearance. This disclosure is further directed to a coating compositioncomprising components derived from renewable resources.

BACKGROUND OF DISCLOSURE

A typical coating finish over a substrate comprises some or all of thefollowing layers: (1) one or more primer layers that provide adhesionand basic protection, and also cover minor surface unevenness of thesubstrate; (2) one or more colored layers, typically pigmented, thatprovide most of the protection, durability and color; and (3) one ormore clearcoat layers that provide additional durability and improvedappearance. A colored topcoat layer can be used in place of the coloredlayer and clearcoat layer.

In some industrial applications, such as coating metal pipes, trucks,large industrial equipments, and large entertainment equipments, it isoften desired to complete the coating process in a short period of timewhile still achieving good adhesion, protection, durability andappearance. Conventional coating compositions for colored layers areoften less optimized for good adhesion directly to metals. In addition,a conventional coating composition typically produces a thin cured drycoating layer that may not have sufficient thickness to cover unevennessof the substrate if only a single layer is used. That could result inundesired appearance. When conventional coatings are applied at a highcoating thickness, surface coating defects such as microfoaming, lowgloss, and sagging may occur. Thick coating layers are typically proneto sagging defects, especially for coating layers applied on verticalsurfaces.

Therefore, there is a need for a coating composition that can produce acoating being sag-free at high coating thicknesses, having gooddirect-to-metal adhesion, and good appearance.

This disclosure is directed to a coating composition comprising a binderconsisting essentially of:

-   -   A) a crosslinkable component consisting essentially of at least        one acrylic polymer having one or more crosslinkable functional        groups;    -   B) a polytrimethylene ether diol having a Mn (number average        molecular weight) in a range of from 500 to 10,000;    -   C) a sag control agent; and    -   D) a crosslinking component consisting essentially of at least        one crosslinking agent having one or more crosslinking        functional groups.

This disclosure is also directed to a substrate coated with the coatingcomposition of this invention.

This disclosure is further directed to a process for forming a sag-freecoating layer on a substrate, said process consisting of the steps of:

-   -   A) applying a coating composition over said substrate forming a        sag-free wet coating layer having a wet coating thickness in a        range of from 10 to 36 mils, wherein said coating composition        comprises a binder consisting essentially of: i) a crosslinkable        component consisting essentially of at least one acrylic polymer        having one or more crosslinkable functional groups; ii) a        polytrimethylene ether diol having a Mn (number average        molecular weight) in a range of from 500 to 10,000; iii) a sag        control agent; and iv) a crosslinking component consisting        essentially of at least one crosslinking agent having one or        more crosslinking functional groups; and    -   B) curing said sag-free wet coating layer to form said sag-free        coating layer.

DETAILED DESCRIPTION

The features and advantages of the present disclosure will be morereadily understood, by those of ordinary skill in the art, from readingthe following detailed description. It is to be appreciated that certainfeatures of the disclosure, which are, for clarity, described above andbelow in the context of separate embodiments, may also be provided incombination in a single embodiment. Conversely, various features of thedisclosure that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any sub-combination.In addition, references in the singular may also include the plural (forexample, “a” and “an” may refer to one, or one or more) unless thecontext specifically states otherwise.

The use of numerical values in the various ranges specified in thisapplication, unless expressly indicated otherwise, are stated asapproximations as though the minimum and maximum values within thestated ranges were both proceeded by the word “about.” In this manner,slight variations above and below the stated ranges can be used toachieve substantially the same results as values within the ranges.Also, the disclosure of these ranges is intended as a continuous rangeincluding every value between the minimum and maximum values.

As used herein:

“Gloss” means surface gloss of a coating surface and is related to theamount of incident light that is reflected at the specular reflectanceangle of the mean of that surface. Gloss can be measured with a specularglossmeter, such as those available from Byk-Gardener, Geretsried,Germany.

“DOI” (Distinctness of Image) is a quantitative measure of coatingappearance that measures the light reflected at and around the specularreflectance angle. It can be determined according to the methoddescribed in ASTM D 5767. DOI can be measured with wave scaninstruments, such as those available from Byk-Gardener, Geretsried,Germany. DOI measures not only the amount of incident light that isreflected at the specular reflectance angle, but also the distributionof the reflected light around the reflectance specular angle, typically±0.3° from the specular angle. A coating surface that gives fuzzy ordistorted image generally produces lower DOI reading. A coatingreflecting 100% of lights at the specular angle gives a DOI reading of100.

The term “sag” or “sagging” refers to coating defects such as droppingline, sagging curtains, tearing drops, or other defects and variationsin coating that cause the coating to be un-smooth. The term “sag-free”or “free of sagging” or “free of sag” means a coating that is free ofsagging defects. It is known to those skilled in the art that a thickwet coating layer tends to form sagging defects.

The term “a coating layer” or “a single coating layer” means a layer ofcoating formed after curing or drying of a wet coating layer of onecoating composition. Such single wet coating layer can be formed by anyconventional coating application methods known to those skilled in theart, such as spraying, brushing, dipping, rolling, or wet draw down.

The term “(meth)acrylate” means methacrylate or acrylate.

The term “two-pack coating composition”, also known as 2K coatingcomposition, refers to a coating composition having two packages thatare stored in separate containers and sealed to increase the shelf lifeof the coating composition during storage. The two packages are mixedjust prior to use to form a pot mix, which has a limited pot life,typically ranging from a few minutes (15 minutes to 45 minutes) to a fewhours (4 hours to 8 hours). The pot mix is then applied as a layer of adesired thickness on a substrate surface, such as an automobile body.After application, the layer dries and cures at ambient or at elevatedtemperatures to form a coating on the substrate surface having desiredcoating properties, such as, adhesion, high gloss, and high DOI.

The term “crosslinkable component” refers to a component having“crosslinkable functional groups” that are functional groups positionedin each molecule of the compounds, oligomer, polymer, the backbone ofthe polymer, pendant from the backbone of the polymer, terminallypositioned on the backbone of the polymer, or a combination thereof,wherein these functional groups are capable of crosslinking withcrosslinking functional groups (during the curing step) to produce acoating in the form of crosslinked structures. One of ordinary skill inthe art would recognize that certain crosslinkable functional groupcombinations would be excluded, since, if present, these combinationswould crosslink among themselves (self-crosslink), thereby destroyingtheir ability to crosslink with the crosslinking functional groups. Aworkable combination of crosslinkable functional groups refers to thecombinations of crosslinkable functional groups that can be used incoating applications excluding those combinations that wouldself-crosslink.

Typical crosslinkable functional groups can include hydroxyl, thiol,isocyanate, thioisocyanate, acetoacetoxy, carboxyl, primary amine,secondary amine, epoxy, anhydride, ketimine, aldimine, or a workablecombination thereof. Some other functional groups such as orthoester,orthocarbonate, or cyclic amide that can generate hydroxyl or aminegroups once the ring structure is opened can also be suitable ascrosslinkable functional groups.

The term “crosslinking component” refers to a component having“crosslinking functional groups” that are functional groups positionedin each molecule of the compounds, oligomer, polymer, the backbone ofthe polymer, pendant from the backbone of the polymer, terminallypositioned on the backbone of the polymer, or a combination thereof,wherein these functional groups are capable of crosslinking with thecrosslinkable functional groups (during the curing step) to produce acoating in the form of crosslinked structures. One of ordinary skill inthe art would recognize that certain crosslinking functional groupcombinations would be excluded, since, if present, these combinationswould crosslink among themselves (self-crosslink), thereby destroyingtheir ability to crosslink with the crosslinkable functional groups. Aworkable combination of crosslinking functional groups refers to thecombinations of crosslinking functional groups that can be used incoating applications excluding those combinations that wouldself-crosslink. One of ordinary skill in the art would recognize thatcertain combinations of crosslinking functional group and crosslinkablefunctional groups would be excluded, since they would fail to crosslinkand produce the film forming crosslinked structures. The crosslinkingcomponent can comprise one or more crosslinking agents that have thecrosslinking functional groups.

Typical crosslinking functional groups can include hydroxyl, thiol,isocyanate, thioisocyanate, acetoacetoxy, carboxyl, primary amine,secondary amine, epoxy, anhydride, ketimine, aldimine, orthoester,orthocarbonate, cyclic amide or a workable combination thereof.

It would be clear to one of ordinary skill in the art that certaincrosslinking functional groups crosslink with certain crosslinkablefunctional groups. Examples of paired combinations of crosslinkable andcrosslinking functional groups can include: (1) amine and protectedamine such as ketimine and aldimine functional groups generallycrosslink with acetoacetoxy, epoxy, or anhydride functional groups; (2)isocyanate, thioisocyanate and melamine functional groups generallycrosslink with hydroxyl, thiol, primary and secondary amine, ketimine,or aldimine functional groups; (3) epoxy functional groups generallycrosslink with carboxyl, primary and secondary amine, ketimine, aldimineor anhydride functional groups; and (4) carboxyl functional groupsgenerally crosslink with epoxy or isocyanate functional groups.

The term “binder” as used herein refers to film forming constituents ofa coating composition. Typically, a binder can comprise a crosslinkablecomponent and a crosslinking component in that the crosslinkablecomponent can react with the crosslinking component to form crosslinkedstructures, such as coating films. The binder in this invention canfurther comprise other polymers, compounds or molecules that areessential for forming crosslinked coatings having desired properties,such as good adhesion, high DOI and free of sagging at high coatingthicknesses. Additional components, such as solvents, pigments,catalysts, rheology modifiers, antioxidants, UV stabilizers andabsorbers, leveling agents, antifoaming agents, anti-cratering agents,or other conventional additives are not included in the term. One ormore of those additional components can be included in the coatingcomposition of this invention.

A substrate suitable for this invention can be a treated metal, baremetal such as blasted steel, aluminum or other metal or alloys. Oneexample of the blasted steel can be the one available from East CoastSteel Inc, Columbia, S.C. 29290, USA.

The coating composition of this disclosure comprises a film formingbinder, herein referred to as the binder. Said binder can consistessentially of:

-   -   A) at least one acrylic polymer having one or more crosslinkable        functional groups;    -   B) a polytrimethylene ether diol having a Mn (number average        molecular weight) in a range of from 500 to 10,000;    -   C) a sag control agent; and    -   D) a crosslinking component containing at least one crosslinking        agent having one or more crosslinking functional groups.

The coating composition of this invention can be applied over asubstrate with conventional coating methods known to those skilled inthe art to form a sag-free coating layer. The sag-free coating layer canhave a wet thickness of more than 10 mils, preferred more than 12 milsand further preferred more than 16 mils. Once cured and dried, thesag-free coating layer can have a dry coating thickness of more than 6mils and a distinctness of image (DOI) of more than 60. In oneembodiment, the dry coating thickness can be more than 6 mils. Inanother embodiment, the dry coating thickness can be more than 7 mils.In yet another embodiment, the DOI can be more than 60. In anotherembodiment, the DOI can be more than 70. In yet another embodiment, theDOI can be more than 80.

The acrylic polymer used in the composition can have a weight averagemolecular weight (Mw) of about 5,000 to 100,000, and a glass transitiontemperature (Tg) in a range of from −40° C. to 80° C. and containfunctional groups or pendant moieties that are reactive with isocyanateor other crosslinking functional groups, such as, for example, hydroxyl,amino, amide, glycidyl, silane and carboxyl groups. The acrylic polymercan have Mw in a range of from 5,000 to 100,000 in one embodiment, in arange of from 6,000 to 80,000 in another embodiment, in a range of from8,000 to 50,000 in yet another embodiment. Tg of the acrylic polymer canbe I a range of from −40° C. to 80° C. in one embodiment, −40° C. to 5°C. in another embodiment, 5° C. to 80° C. in yet another embodiment. TheTg of the acrylic polymer can be measured experimentally or calculatedaccording to the Fox Equation. These acrylic polymers can be straightchain polymers, branched polymers, block copolymers, graft polymers,graft terpolymers or core shell polymers.

The acrylic polymers can be polymerized from a plurality of monomers,such as acrylates, methacrylates or derivatives thereof.

Suitable monomers can include linear alkyl(meth)acrylates having 1 to 12carbon atoms in the alkyl group, cyclic or branched alkyl(meth)acrylateshaving 3 to 12 carbon atoms in the alkyl group, includingisobornyl(meth)acrylate, styrene, alpha methyl styrene, vinyl toluene,(meth)acrylonitrile, (meth)acryl amides and monomers that providecrosslinkable functional groups, such as, hydroxy alkyl(meth)acrylateshaving 1 to 4 carbon atoms in the alkyl group, glycidyl(meth)acrylate,amino alkyl(meth)acrylates having 1 to 4 carbon atoms in the alkylgroup, (meth)acrylic acid, and alkoxy silyl alkyl(meth)acrylates, suchas, trimethoxysilylpropyl(meth)acrylate. Particularly, monomers havinginherent low Tg properties can be suitable for deriving low Tg acrylicpolymers when desired. Examples of low Tg monomers include butylacrylate (Tg about −54° C.), 2-ethylhexyl acrylate (Tg about −50° C.),ethyl acrylate (Tg about −24° C.), isobutyl acrylate (Tg about −24° C.),and 2-ethylhexyl methacrylate (Tg about −10° C.). Monomers havinginherent high Tg properties can be suitable for deriving high Tg acrylicpolymers when desired. Examples of such high Tg monomers can includestyrene (Tg: 100° C.), methyl methacrylate (MMA) (Tg: about 105° C.),isobornyl methacrylate (IBOMA) (Tg: about 165° C.), isobornyl acrylate(IBOA) (Tg: about 94° C.), cyclohexyl methacrylate (CHMA) (Tg: about 83°C.), and isobutyl methacrylate (IBMA) (Tg: about 55° C.). Theabovementioned Tg values are derived from published literatures and arecommonly accepted in the industry. Theoretical Tgs of the acrylicpolymers can be predicted using the Fox equation based on Tgs of themonomers. Actual Tg's of the finished polymers can be measured by DSC(Differential Scanning Calorimetry, also available as ASTM D3418/E1356).

Suitable monomers can also include, for example, hydroxyalkyl esters ofalpha,beta-olefinically unsaturated monocarboxylic acids with primary orsecondary hydroxyl groups. These may, for example, comprise thehydroxyalkyl esters of acrylic acid, methacrylic acid, crotonic acidand/or isocrotonic acid. Examples of suitable hydroxyalkyl esters ofalpha,beta-olefinically unsaturated monocarboxylic acids with primaryhydroxyl groups can include hydroxyethyl(meth)acrylate,hydroxypropyl(meth)acrylate, hydroxybutyl(meth)acrylate,hydroxyamyl(meth)acrylate, hydroxyhexyl(meth)acrylate. Examples ofsuitable hydroxyalkyl esters with secondary hydroxyl groups can include2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate,3-hydroxybutyl(meth)acrylate. Low Tg monomers, such as hydroxylfunctional monomers, such as 2-hydroxyethyl acrylate (Tg: −15° C.) andhydroxypropyl acylate (Tg: −7° C.) can be useful in decreasing Tg of theacrylic polymer to produce low Tg acrylic polymers and providing thecrosslinkable functional groups. When high Tg acrylic polymers aredesired, one or more high Tg monomers can be included. Examples of suchhigh Tg hydroxyl monomers can include hydroxyethyl methacrylate (HEMA)(Tg: about 55° C.) and hydroxypropyl methacrylate (HPMA) (Tg: about 76°C.).

Suitable monomers can also include monomers that are reaction productsof alpha,beta-unsaturated monocarboxylic acids with glycidyl esters ofsaturated monocarboxylic acids branched in alpha position, for examplewith glycidyl esters of saturated alpha-alkylalkanemonocarboxylic acidsor alpha,alpha′-dialkylalkanemonocarboxylic acids. These can comprisethe reaction products of (meth)acrylic acid with glycidyl esters ofsaturated alpha,alpha-dialkylalkanemonocarboxylic acids with 7 to 13carbon atoms per molecule, particularly preferably with 9 to 11 carbonatoms per molecule. These reaction products can be formed before, duringor after copolymerization reaction of the acrylic polymer.

Suitable monomers can further include monomers that are reactionproducts of hydroxyalkyl(meth)acrylates with lactones.Hydroxyalkyl(meth)acrylates which can be used include, for example,those stated above. Suitable lactones can include, for example, thosethat have 3 to 9 carbon atoms in the ring, wherein the rings can alsocomprise different substituents. Examples of lactones can includegamma-butyrolactone, delta-valerolactone, epsilon-caprolactone,beta-hydroxy-beta-methyl-delta-valerolactone, lambda-laurolactone or amixture thereof. In one example, the reaction products can comprisethose prepared from 1 mole of a hydroxyalkyl ester of analpha,beta-unsaturated monocarboxylic acid and 1 to 5 moles, preferablyon average 2 moles, of a lactone. The hydroxyl groups of thehydroxyalkyl esters can be modified with the lactone before, during orafter the copolymerization reaction.

Suitable monomers can also include unsaturated monomers such as, forexample, allyl glycidyl ether, 3,4-epoxy-1-vinylcyclohexane,epoxycyclohexyl(meth)acrylate, vinyl glycidyl ether andglycidyl(meth)acrylate, that can be used to provide the acrylic polymerwith glycidyl groups. In one example, glycidyl(meth)acrylate can beused.

Suitable monomers can also include monomers that are free-radicallypolymerizable, olefinically unsaturated monomers which, apart from atleast one olefinic double bond, do not contain additional functionalgroups. Such monomers include, for example, esters of olefinicallyunsaturated carboxylic acids with aliphatic monohydric branched orunbranched as well as cyclic alcohols with 1 to 20 carbon atoms.Examples of the unsaturated carboxylic acids can include acrylic acid,methacrylic acid, crotonic acid and isocrotonic acid. In one embodiment,esters of (meth)acrylic acid can be used. Examples of esters of(meth)acrylic acid can include methyl acrylate, ethyl acrylate,isopropyl acrylate, tert.-butyl acrylate, n-butyl acrylate, isobutylacrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate andthe corresponding methacrylates. Examples of esters of (meth)acrylicacid with cyclic alcohols can include cyclohexyl acrylate,trimethylcyclohexyl acrylate, 4-tert.-butylcyclohexyl acrylate,isobornyl acrylate and the corresponding methacrylates.

Suitable monomers can also include unsaturated monomers that do notcontain additional functional groups for example, vinyl ethers, such as,isobutyl vinyl ether and vinyl esters, such as, vinyl acetate, vinylpropionate, vinyl aromatic hydrocarbons, preferably those with 8 to 9carbon atoms per molecule. Examples of such monomers can includestyrene, alpha-methylstyrene, chlorostyrenes, 2,5-dimethylstyrene,p-methoxystyrene, vinyl toluene. In one embodiment, styrene can be used.

Suitable monomers can also include small proportions of olefinicallypolyunsaturated monomers. These olefinically polyunsaturated monomersare monomers having at least 2 free-radically polymerizable double bondsper molecule. Examples of these olefinically polyunsaturated monomerscan include divinylbenzene, 1,4-butanediol diacrylate, 1,6-hexanedioldiacrylate, neopentyl glycol dimethacrylate, and glyceroldimethacrylate.

The acrylic polymers of this disclosure can generally be polymerized byfree-radical copolymerization using conventional processes well known tothose skilled in the art, for example, bulk, solution or beadpolymerization, in particular by free-radical solution polymerizationusing free-radical initiators.

The acrylic polymer can contain (meth)acrylamides. Typical examples ofsuch acrylic polymers can be polymerized from monomers including(meth)acrylamide. In one example, such acrylic polymer can bepolymerized from (meth)acrylamide and alkyl(meth)acrylates, hydroxyalkyl(meth)acrylates, (meth)acrylic acid and one of the aforementionedolefinically unsaturated monomers.

The polytrimethylene ether diol suitable for the coating composition ofthis disclosure can have a number average molecular weight (Mn) in therange of from 500 to 10,000, preferably 500 to 8,000, even preferably500 to 4,000. The polytrimethylene ether diol has a Tg of about −75° C.,a polydispersity in the range of from 1.1 to 2.1 and a hydroxyl numberin the range of from 20 to 200.

Suitable polytrimethylene ether diol can be prepared by anacid-catalyzed polycondensation of 1,3-propanediol, such as described inU.S. Pat. Nos. 6,977,291 and 6,720,459. The polytrimethylene ether diolcan also be prepared by a ring opening polymerization of a cyclic ether,oxetane, such as described in J. Polymer Sci., Polymer Chemistry Ed. 28,449 to 444 (1985). The polycondensation of 1,3-propanediol is preferredover the use of oxetane since the diol is a less hazardous, stable, lowcost, commercially available material and can be prepared by use ofpetro chemical feed-stocks or renewable resources.

A bio-route via fermentation of a renewable resource can be used toobtain the 1,3-propanediol. One example of renewable resources is cornsince it is readily available and has a high rate of conversion to1,3-propanediol and can be genetically modified to improve yields to the1,3-propanediol. Examples of typical bio-route can include thosedescribed in U.S. Pat. No. 5, 686,276, U.S. Pat. No. 5,633,362 and U.S.Pat. No. 5,821,092.

Copolymers of polytrimethylene ether diol also can be suitable for thecoating composition of this disclosure. Examples of such suitablecopolymers of polytrimethylene ether diol can be prepared bycopolymerizing 1,3-propanediol with another diol, such as, ethane diol,hexane diol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol,trimethylol propane and pentaerythritol. In one example, the copolymersof polytrimethylene ether diol can be polymerized from monomers have1,3-propanediol in a range of from 50% to 99%. In another example, thecopolymers of polytrimethylene ether diol can be polymerized frommonomers have 1,3-propanediol in a range of from 60% to 99%. In yetanother example, the copolymers of polytrimethylene ether diol can bepolymerized from monomers have 1,3-propanediol in a range of from 70% to99%.

A blend of a high and a low molecular weight polytrimethylene ether diolcan be used. In one example, the high molecular weight polytrimethyleneether diol can have an Mn in a range of from 1,000 to 4,000 and the lowmolecular weight polytrimethylene ether diol can have an Mn in a rangeof from 150 to 500. The average Mn of the blended polytrimethylene etherdiol can be in a range of from 500 to 4,000. In another example, thehigh molecular weight polytrimethylene ether diol can have an Mn in arange of from 1,000 to 4,000 and the low molecular weightpolytrimethylene ether diol can have an Mn in a range of from 150 to 500and the average Mn of the blend can be in a range of from 500 to 3,000.

Blends of the polytrimethylene ether diol and other cycloaliphatichydroxyl containing either branched or linear oligomers can be used.Such hydroxyl containing oligomers are known to those skilled in theart. Examples of such hydroxyl containing oligomers can include thosedisclosed by Barsotti, et al. in U.S. Pat. No. 6,221,494.

Sag control agent, hereafter referred to as SCA, is typically used tocontrol sagging and therefore improving appearance of a coating. In anexample, said SCA can be a reaction product of an isocyanate and anamine. Said SCA can be produced with conventional methods known to thoseskilled in the art. Said SCA can be produced in the presence or in theabsence of one or more acrylic polymers or a binder. One example of suchconventional methods is described in U.S. Pat. No. 4,677,028.Microstructures of the SCA can be modified by selecting the isocyanateand the amine, and synthetic conditions. The SCA can also be made in away that they are soluble in a polar solvent such as N-methylpyrrolidone to form a SCA solution. Such SCA solution can beconveniently added directly to a coating to achieve the desired rheologyor sag control effect. One example of such SCA solution is commerciallyavailable as Byk® 410 from Byk Chemie GmbH, Wesel, Germany, sold underrespective registered trademark.

Suitable isocyanates for synthesizing said SCA can include blocked orun-blocked aliphatic, cycloaliphatic, heterocyclo, or aromatic di-, tri-or multivalent isocyanates. Examples of suitable diisocyanates caninclude 1,6-hexamethylene diisocyanate,2,2,4-trimethylhexane-1,6-diisocyanate,2,4,4-trimethylhexane-1,6-diisocyanate, cyclohexyl-1,4-diisocyanate,isophoron diisocyanate, the adduct of 1 molecule of 1,4-butanediol and 2molecules of isophoron diisocyanate, the adduct of 1 molecule of1,4-butanediol and 2 molecules of hexamethylene diisocyanate,dicyclohexylmethane-4,4′-diisocyanate, xylylene diisocyanate,1,3,5-trimethyl-2,4-bis(isocyanatomethyl)benzene, toluene diisocyanate,diphenylmethane-4,4′-diisocyanate, adducts of hexamethylenediisocyanate, adducts of isophoron diisocyanate, and adducts of toluenediisocyanate. Isocyanurate-trimers that built up from diisocyantes canalso be suitable. A combination of the isocyantes can also be suitable.Any of the isocyanates mentioned in the examples above can be blocked orunblocked.

Amines suitable for the SCA can include primary amines. Examples ofprimary amines can include benzyl amine, ethylamine, n-propylamine,2-propylamine, n-butylamine, 2-butylamine, t-butylamine, n-pentylamine,α-methylbutylamine, α-ethylpropylamine, β-ethylbutylamine, hexylamine,octylamine, decylamine, stearylamine, cyclohexylamine, and aniline. Acombination of the amines can also be suitable.

The SCAs produced by aforementioned process are typically free fromun-reacted iscocyanates since excess amount of amine is normally used.

Typically, the coating composition of this invention can comprise in arange of from 0.1% to 10% of the SCA, weight percent of the total weightof the binder. The coating composition can comprise in a range of from0.1% to 10% of the SCA in one example, 0.2% to 8% in another example,0.2% to 5% in yet another example, weight percent of the total weight ofthe binder. If a SCA solution such as BYK® 410 is used, polarity ofsolvent or solvent mix may need to be adjusted according tomanufacturer's instruction so the SCA can be dispersed into the coatingwithout separation.

The crosslinking agents that are suitable for the coating composition ofthis disclosure include compounds having crosslinking functional groups.Examples of such compounds can be organic polyisocyanates. Examples oforganic polyisocyanates include aliphatic polyisocyanates,cycloaliphatic polyisocyanates, aromatic polyisocyanates and isocyanateadducts.

Examples of suitable aliphatic, cycloaliphatic and aromaticpolyisocyanates that can be used include the following: 2,4-toluenediisocyanate, 2,6-toluene diisocyanate (“TDI”), 4,4-diphenylmethanediisocyanate (“MDI”), 4,4′-dicyclohexyl methane diisocyanate (“H12MDI”),3,3′-dimethyl-4,4′-biphenyl diisocyanate (“TODI”), 1,4-benzenediisocyanate, trans-cyclohexane-1,4-diisocyanate, 1,5-naphthalenediisocyanate (“NDI”), 1,6-hexamethylene diisocyanate (“HDI”), 4,6-xylenediisocyanate, isophorone diisocyanate, (“IPDI”), other aliphatic orcycloaliphatic di-, tri- or tetra-isocyanates, such as, 1,2-propylenediisocyanate, tetramethylene diisocyanate, 2,3-butylene diisocyanate,octamethylene diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate,dodecamethylene diisocyanate, omega-dipropyl ether diisocyanate,1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate,1,4-cyclohexane diisocyanate, 4-methyl-1,3-diisocyanatocyclohexane,dicyclohexylmethane-4,4′-diisocyanate, 3,3′-dimethyl-dicyclohexylmethane4,4′-diisocyanate, polyisocyanates having isocyanurate structural units,such as, the isocyanurate of hexamethylene diisocyanate and theisocyanurate of isophorone diisocyanate, the adduct of 2 molecules of adiisocyanate, such as, hexamethylene diisocyanate, uretidiones ofhexamethylene diisocyanate, uretidiones of isophorone diisocyanate and adiol, such as, ethylene glycol, the adduct of 3 molecules ofhexamethylene diisocyanate and 1 molecule of water, allophanates,trimers and biurets, for example, of hexamethylene diisocyanate,allophanates, trimers and biurets, for example, of isophoronediisocyanate and the isocyanurate of hexane diisocyanate. MDI, HDI, TDIand isophorone diisocyanate are preferred because of their commercialavailability.

Tri-functional isocyanates also can be used, such as, triphenyl methanetriisocyanate, 1,3,5-benzene triisocyanate, 2,4,6-toluene triisocyanate.Trimers of diisocyanates, such as, the trimer of hexamethylenediisocyanate, sold as Tolonate® HDT from Rhodia Corporation and thetrimer of isophorone diisocyanate are also suitable.

An isocyanate functional adduct can be used, such as, an adduct of analiphatic polyisocyanate and a polyol or an adduct of an aliphaticpolyisocyanate and an amine. Also, any of the aforementionedpolyisocyanates can be used with a polyol to form an adduct. Polyols,such as, trimethylol alkanes, particularly, trimethylol propane orethane can be used to form an adduct.

The coating composition of this invention can contain in a range of from1% to 50% by weight in one embodiment, in a range of from 10% to 40% byweight in another embodiment, in a range of from 20% to 40% by weight inyet another embodiment, based on the weight of the binder, of acrylicNAD (non-aqueous dispersed) resins. These NAD resins typically caninclude high molecular weight resins having a crosslinked acrylic corewith a Tg between 20 to 100° C. and attached to the core are low Tgstabilizer segments. Examples of such NAD resins can include thosedisclosed in U.S. Pat. No. 4,591,533, U.S. Pat. No. 5,010,140 and U.S.Pat. No. 5,763,528.

Typically, a catalyst can be used in the coating composition of thisinvention to reduce curing time and to allow curing of the coatingcomposition at ambient temperatures. The ambient temperatures aretypically referred to as temperatures in a range of from range of 18° C.to 35° C. Typical catalysts include organic metal salts, such as,dibutyl tin dilaurate, dibutyl tin diacetate, dibutyl tin dichloride,dibutyl tin dibromide, zinc naphthenate; compounds containing tertiaryamino groups, such as, triethylamine; triphenyl boron, tetraisopropyltitanate, triethanolamine titanate chelate, dibutyl tin dioxide, dibutyltin dioctoate, tin octoate, aluminum titanate, aluminum chelates,zirconium chelate, hydrocarbon phosphonium halides, such as, ethyltriphenyl phosphonium iodide and other such phosphonium salts, and othercatalysts or mixtures thereof known to those skilled in the art.

The coating composition of this invention can comprise one or moresolvents. Typically the coating composition can comprise up to 80% byweight, based on the weight of the coating composition, of one or moresolvents. Typically, the coating composition of this invention can havea solid content in a range of from 20% to 80% by weight in one example,in a range of from 50% to 80% by weight in another example and in arange of from 60% to 80% by weight in yet another example, all based onthe total weight of the coating composition. The coating composition ofthis invention can also be formulated at 100% solids by using a lowmolecular weight acrylic resin reactive diluent known to those skilledin the art.

Any typical organic solvents can be used to form the coating compositionof this invention. Examples of solvents can include, but not limited to,aromatic hydrocarbons, such as, toluene, xylene; ketones, such as,acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketoneand diisobutyl ketone; esters, such as, ethyl acetate, n-butyl acetate,isobutyl acetate and a combination thereof.

Typically, when the coating composition of this invention is utilized asa pigmented coating composition, it contains pigments in a pigment tobinder weight ratio of 1/100 to 350/100. The coating composition can beused as a basecoat or topcoat, such as a colored topcoat. Conventionalinorganic and organic colored pigments, metallic flakes and powders,such as, aluminum flake and aluminum powders; special effects pigments,such as, coated mica flakes, coated aluminum flakes colored pigments, ora combination thereof can be used. Transparent pigments or pigmentshaving the same refractive index as the cured binder can also be used.Such transparent pigments can be used in a pigment to binder weightratio of 0.1/100 to 5/100. One example of such transparent pigment issilica.

The coating composition of this invention can also comprise one or moreultraviolet light stabilizers in the amount of 0.1% to 10% by weight,based on the weight of the binder. Examples of such ultraviolet lightstabilizers can include ultraviolet light absorbers, screeners,quenchers, and hindered amine light stabilizers. An antioxidant can alsobe added to the coating composition, in the amount of about 0.1% to 5%by weight, based on the weight of the binder.

Typical ultraviolet light stabilizers that are suitable for thisinvention can include benzophenones, triazoles, triazines, benzoates,hindered amines and mixtures thereof. A blend of hindered amine lightstabilizers, such as Tinuvin® 328 and Tinuvin®123, all commerciallyavailable from Ciba Specialty Chemicals, Tarrytown, N.Y., underrespective registered trademark, can be used.

Typical ultraviolet light absorbers that are suitable for this inventioncan include hydroxyphenyl benzotriazoles, such as,2-(2-hydroxy-5-methylphenyl)-2H-benzotrazole,2-(2-hydroxy-3,5-di-tert.amyl-phenyl)-2H-benzotriazole,2[2-hydroxy-3,5-di(1,1-dimethylbenzyl)phenyl]-2H-benzotriazole, reactionproduct of 2-(2-hydroxy-3-tert.butyl-5-methylpropionate)-2H-benzotriazole and polyethylene ether glycol having aweight average molecular weight of 300,2-(2-hydroxy-3-tert.butyl-5-iso-octyl propionate)-2H-benzotriazole;hydroxyphenyl s-triazines, such as,2-[4((2,-hydroxy-3-dodecyloxy/tridecyloxypropyl)-oxy)-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine,2-[4(2-hydroxy-3-(2-ethylhexyl)-oxy)-2-hydroxyphenyl]-4,6-bis(2,4-dimethylpenyl)1,3,5-triazine,2-(4-octyloxy-2-hydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine;hydroxybenzophenone U.V. absorbers, such as, 2,4-dihydroxybenzophenone,2-hydroxy-4-octyloxybenzophenone, and2-hydroxy-4-dodecyloxybenzophenone.

Typical hindered amine light stabilizers can includeN-(1,2,2,6,6-pentamethyl-4-piperidinyl)-2-dodecyl succinimide,N(1acetyl-2,2,6,6-tetramethyl-4-piperidinyl)-2-dodecyl succinimide,N-(2hydroxyethyl)-2,6,6,6-tetramethylpiperidine-4-ol-succinic acidcopolymer, 1,3,5 triazine-2,4,6-triamine,N,N′″-[1,2-ethanediybis[[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1-propanediyl]]bis[N,N′″-dibutyl-N′,N′″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)],poly-[[6-[1,1,3,3-tetramethylbutyl)-amino]-1,3,5-trianzine-2,4-diyl][2,2,6,6-tetramethylpiperidinyl)-imino]-1,6-hexane-diyl[(2,2,6,6-tetramethyl-4-piperidinyl)-imino]),bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate,bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate,bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidinyl)sebacate,bis(1,2,2,6,6-pentamethyl-4-piperidinyl)[3,5bis(1,1-dimethylethyl-4-hydroxy-phenyl)methyl]butylpropanedioate,8-acetyl-3-dodecyl-7,7,9,9,-tetramethyl-1,3,8-triazaspiro(4,5)decane-2,4-dione,and dodecyl/tetradecyl-3-(2,2,4,4-tetramethyl-2I-oxo-7-oxa-3,20-diazaldispiro(5.1.11.2)henicosan-20-yl)propionate.

Typical antioxidants that are suitable for this invention can includetetrakis[methylene(3,5-di-tert-butylhydroxy hydrocinnamate)]methane,octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate,tris(2,4-di-tert-butylphenyl) phosphite,1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trioneand benzenepropanoic acid, 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-C7-C9branched alkyl esters. Typically useful antioxidants can also includehydroperoxide decomposers, such as Sanko® HCA(9,10-dihydro-9-oxa-10-phosphenanthrene-10-oxide), triphenyl phosphateand other organo-phosphorous compounds, such as, Irgafos® TNPP from CibaSpecialty Chemicals, Irgafos® 168, from Ciba Specialty Chemicals,Ultranox® 626 from GE Specialty Chemicals, Mark PEP-6 from Asahi Denka,Mark HP-10 from Asahi Denka, Irgafos® P-EPQ from Ciba SpecialtyChemicals, Ethanox 398 from Albemarle, Weston 618 from GE SpecialtyChemicals, Irgafos® 12 from Ciba Specialty Chemicals, Irgafos® 38 fromCiba Specialty Chemicals, Ultranox® 641 from GE Specialty Chemicals andDoverphos® S-9228 from Dover Chemicals.

The coating compositions of this invention can comprise conventionalcoating additives. Examples of such additives can include wettingagents, leveling and flow control agents, for example, Resiflow®S(polybutylacrylate), BYK® 320 and 325 (high molecular weightpolyacrylates), BYK® 347 (polyether-modified siloxane) under respectiveregistered tradmarks, leveling agents based on (meth)acrylichomopolymers; rheological control agents, such as highly dispersesilica, or fumed silica; thickeners, such as partially crosslinkedpolycarboxylic acid or polyurethanes; and antifoaming agents. Theadditives are used in conventional amounts familiar to those skilled inthe art.

The coating compositions according to this invention can further containreactive low molecular weight compounds as reactive diluents that arecapable of reacting with the crosslinking agent. For example, lowmolecular weight polyhydroxyl compounds, such as, ethylene glycol,propylene glycol, trimethylolpropane and 1,6-dihydroxyhexane can beused.

Depending upon the type of crosslinking agent, the coating compositionof this invention can be formulated as one-pack (1K) or two-pack (2K)coating composition. If polyisocyanates with free isocyanate groups areused as the crosslinking agent, the coating composition can beformulated as a two-pack coating composition in that the crosslinkingagent is mixed with other components of the coating composition onlyshortly before coating application. If blocked polyisocyanates are, forexample, used as the crosslinking agent, the coating compositions can beformulated as a one-pack (1K) coating composition. The coatingcomposition can be further adjusted to spray viscosity with organicsolvents as determined by those skilled in the art before being applied.

In a typical two-pack coating composition comprising two packages, thetwo packages are mixed together shortly before application. The firstpackage typically can contain the binder including the polymer havingone or more hydroxyl crosslinkable functional groups, thepolytrimethylene ether diol and the sag control agent. Optionally, oneor more pigments can be dispersed in the first package usingconventional dispersing techniques, for example, ball milling, sandmilling, and attritor grinding. The second package can contain thecrosslinking agent, such as, a polyisocyanate crosslinking agent, andsolvents.

The coating composition according to the disclosure can be suitable forvehicle and industrial coating and can be applied using known processes.In the context of vehicle coating, the coating composition can be usedboth for vehicle original equipment manufacturing (OEM) coating and forrepairing or refinishing coatings of vehicles and vehicle parts. Curingof the coating composition can be accomplished at ambient temperatures,such as temperatures in a range of from 18° C. to 35° C., or at elevatedtemperatures, such as at temperatures in a range of from 35° C. to 150°C. Typical curing temperatures of 20° C. to 80° C., in particular of 20°C. to 60° C., can be used for vehicle repair or refinish coatings.

The coating composition can be applied by conventional techniques, suchas, spraying, electrostatic spraying, dipping, brushing, and flowcoating. Typically, the coating can be applied to a substrate to form asag-free coating layer having a wet coating thickness, also known as wetfilm thickness (wft), in a range of, in one example from 5 to 36 mils(about 127 to 914 microns), in another example from 6 to 36 mils (about152 to 914 microns), in yet another example from 7 to 36 mils (about 178to 914 microns), in yet another example from 8 to 36 mils (about 203 to914 microns), in yet another example from 10 to 36 mils (about 254 to914 microns), in yet another example from 12 to 36 mils (about 305 to914 microns), in yet another example from 14 to 36 mils (about 356 to914 microns), and in yet further example from 16 to 36 mils (about 406to 914 microns). After curing and drying, dry coating thickness can betypically in a range of from 2 to 20 mils. A dry coating thickness canbe 2 to 20 mils in one example, 4 to 20 mils in another example, 6 to 20mils in yet another example, and 7 to 20 mils in further anotherexample.

The use of polytrimethylene ether diol in coating compositions has beendescribed in U.S. Pat. Nos. 6,875,514 and 7,169,475. Thepolytrimethylene ether diol is believed to provide improved flexibilityto a coating therefore improving chip resistance. The coatings disclosedin the above mentioned US patents generally require additional sandingor buffing.

Sag control agents (SCAs) that are reaction products of primary aminesand triisocyanates have been disclosed in aforementioned U.S. Pat. No.4,677,028. However, coatings disclosed in the U.S. Pat. No. 4,677,028started showing sagging at a dry coating thickness of about 2.2 mils (55microns) to 3.9 mils (100 microns).

The Applicants unexpectedly discovered that a combination ofpolytrimethylene ether diol and SCA can produce a coating layer that hassag-free wet coating thickness higher than 10 mils (about 254 microns)and a corresponding dry coating thickness of more than 6 mils (about 152microns) with excellent adhesion, high gloss and good DOI.

Advantages of the coating composition of this invention can includedirect to metal coating application without a primer layer and high dryfilm build. Some substrates, such as blasted steel, may have certainsurface profile with surface unevenness in a range of 1-5 mils. A thincoating with a dry coating thickness of about 1-5 mils may not cover thesurface unevenness resulting in uneven coating and unacceptable coatingappearance. To form a 5 mil dry coating layer, typically a wet coatinglayer having a wet coating thickness of 10 mils or more can be needed.As described in aforementioned U.S. Pat. No. 4,677,028, coatingcompositions typically start to show sagging when a dry coatingthickness reaches about 2.2 mils (55 microns) to 3.9 mils (100 microns)even in the presence of sag control agents. To achieve desired total dryfilm thickness and desired appearance, in a traditional process,multiple coating layers have to be applied in succession wherein eachcoating layer needs to be dried before a subsequent coating layer can beapplied thereon. Sanding may be needed between coatings. Suchtraditional process requires multiple steps to apply multiple coatlayers and can be time consuming leading to low productivity. Thecoating composition of this invention can be used to directly apply overa metal substrate producing a sag-free coating layer having a drycoating thickness of 6 mils or more. In one example, a sage-free coatinglayer of 6 mils can be produced by applying a single layer of thecoating composition over a substrate. In another example, a sage-freecoating layer of 7 mils can be produced by applying a single layer ofthe coating composition over a substrate. The use of the coatingcomposition of this invention can provide improvement to coatingproductivity.

This invention is also directed to a process for forming a sag-freecoating layer on a substrate. Said process can consist of the steps of:

-   -   A) applying a coating composition over said substrate forming a        sag-free wet coating layer having a wet coating thickness in a        range of from 10 to 36 mils, wherein said coating composition        comprises a binder consisting essentially of: i) a crosslinkable        component consisting essentially of at least one acrylic polymer        having one or more crosslinkable functional groups; ii) a        polytrimethylene ether diol having a Mn (number average        molecular weight) in a range of from 500 to 10,000; iii) a sag        control agent; and iv) a crosslinking component consisting        essentially of at least one crosslinking agent having one or        more crosslinking functional groups; and    -   B) curing said sag-free wet coating layer to form said sag-free        coating layer.

Said sag-free wet coating layer can have a wet coating thickness in arange of from 10 to 36 mils in one embodiment, 12 to 36 mils in anotherembodiment, and 16 to 36 mils in yet another embodiment. The sag-freecoating formed by this invention can have a dry coating thickness in arange of from 2 to 20 mils. The dry coating thickness can be, in oneembodiment in a range of from 2 to 20 mils, in another embodiment in arange of from 6 to 20 mils and in yet another embodiment in a range offrom 7 to 20 mils.

The sag-free coating layer formed by this invention can have adistinctness of image (DOI) in a range of from 60 to 100 in oneembodiment, 70 to 100 in another embodiment, and 80 to 100 in yetanother embodiment.

One advantage of this invention is that a sag-free coating layer of highthickness, such as the one having dry coating thickness of more than 6mils can be formed with a single wet coating layer without the needs forrepeatedly drying and applying multiple coating layers.

Testing Procedures

Dry Film Thickness—test method ASTM D4138

Viscosity—can be measured using (1) Zahn Viscosity as determined using a#1 Zahn cup according to ASTM D 1084 Method D; (2) Gardner-Holdt Letterscale according to ASTM Dl 545; or (3) Brookfield viscometer; asspecified.

Tg (glass transition temperature) of a polymer is determined accordingto ASTM D-3418 (1988) or calculated according to the Fox Equation.

Molecular weight and hydroxyl number of the polytrimethylene ether diolare determined according to ASTM E222.

Molecular weights Mw and Mn and the polydispersity (Mw/Mn) of theacrylic polymer and other polymers are determined by GPC (Gel PermeationChromatography) using polystyrene standards and tetrahydrofuran as thesolvent.

Cross-Hatch Adhesion Test—The cross hatch tape test is primarilyintended for use in the laboratory. A cross-hatch pattern is createdusing a special cross-hatch cutter with multiple preset blades can beused to make parallel incisions with proper space. After the tape hasbeen applied and pulled off, the cut area is inspected and rated. Theforegoing test is based on a standard method for the application andperformance of these adhesion tests available in ASTM D3359 B. Adhesioncan be rated on a sliding scale, which ranges from 0B (no adhesion,i.e., total failure) to 5B (complete adhesion, i.e., total success). Arating of 3B and higher is preferable and a rating of 9 and higher ismore preferable. A device described in U.S. Patent Publication No.2006/0042724, published on Mar. 2, 2006, filed on Jun.16, 2005 with anapplication Ser. No.11/154,487, can be used to create properly spacedand parallel incisions into the coating.

Dry to touch time—Dry to touch time is determined by ASTM D1640.

Tack Free Time—Tack free time was determined with Mechanical Test Methodaccording to ASTM D1640-95. Said mechanical test method was originallydescribed in U.S. Pat. No. 2,406,989.

DOI—Instrumental measurement of distinctness of Image (DOI) gloss ofcoating surfaces is determined according to ASTM D 5767.

Sag measurement—Sagging of coatings was measured according to ASTM D4400 using a multinotch applicator. In brief, a coating composition isapplied to a panel to form coating stripes at different thickness usingthe multinotch applicator. The panel is then positioned vertically withthe coating stripes across the panel horizontally. Each stripe isvisually examined for sagging. Film thickness of the thickest coatingstripe that is sag free is recorded in mils (1 mil=0.0254 mm=0.001inch). Wet film thickness, also referred to as wet coating thickness,can be determined based on indications of the multinotch applicator usedfor coating or with other instruments or methods known to those skilledin the art. Examples of commercially available instruments include wetfilm thickness measuring wheels or combs. Dry film thickness can bedetermined with aforementioned method.

Gloss—measured with standard test method for specular gloss according toASTM D 523.

In the following examples, all parts and percentages are on a weightbasis unless otherwise indicated. “Mw” weight average molecular weightand “Mn” means number average molecular weight.

EXAMPLES

The present invention is further defined in the following Examples. Itshould be understood that these Examples, while indicating preferredembodiments of the invention, are given by way of illustration only.From the above discussion and these Examples, one skilled in the art canascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various uses andconditions.

Procedure 1: Preparation of Acrylic Polymers (A) Low Tg Acrylic Polymer

Low Tg acrylic polymers were formed by free-radical copolymerizationusing conventional processes well known to those skilled in the art. Theprocess is briefly described here. Charge to a reactor equipped with astirrer, reflux condenser and under nitrogen 13.7 parts t-butylacetate.Heat to reflux, at approximately 96° C. Premix a monomer mixture of 8.8parts methyl methacrylate, 5.9 parts styrene, 11.7 parts hydroxyethylmethacrylate, 20.5 parts n-butyl acrylate, 11.7 parts 2-ethylhexylmethacrylate, 1.2 parts t-butylacetate. Premix an initiator mixture of3.4 parts Vazo® 67 (Vazo® 67 is available from E. I. DuPont de Nemoursand Company, Wilmington, Del., USA, and under respective registeredtrademark) and 23.2 parts t-butylacetate. Feed monomer mixture over 390minutes at reflux simultaneously with the initiator mixture. Feedinitiator mixture over 400 minutes. After the initiator mixture feed wascomplete, hold 30 minutes at reflux. Then cool to room temperature. Theacrylic polymer resin produced has a calculated Tg of +2.2° C., 46.7 wt% solids, Gardner-Holdt viscosity B in Gardner-Holdt Letter scaleaccording to ASTM D1545, and weight average molecular weight (Mw) of9455.

(B) High Tg Acrylic Polymer

High Tg acrylic polymers were formed by similar free-radicalcopolymerization as described above with different monomer ratio asdescribed below. Charge to a reactor equipped with a stirrer, refluxcondenser and under nitrogen 13.7 parts t-butylacetate. Heat to reflux,at approximately 96° C. Premix a monomer mixture of 14.6 parts methylmethacrylate, 5.9 parts styrene, 11.7 parts hydroxyethyl methacrylate,14.6 parts n-butyl acrylate, 11.7 parts 2-ethylhexyl methacrylate, 1.2parts t-butylacetate. Premix an initiator mixture of 3.4 parts Vazo® 67(Vazo® 67 is available from E. I. DuPont de Nemours and Company,Wilmington, Del., USA, and under respective registered trademark) and23.2 parts t-butylacetate. Feed monomer mixture over 360 minutes atreflux simultaneously with the initiator mixture. Feed initiator mixtureover 390 minutes. After the initiator mixture feed was complete, hold 60minutes at reflux. Then cool to room temperature.

The acrylic polymer resin produced herein had the followingcharacteristics: a calculated Tg of +17.6° C., solids 60%, Gardner-Holdtviscosity Y+¼, and weight average molecular weight (Mw) of 10,000.

Procedure 2: Preparation of Sag Control Agent

(A) SCA in Low Tg Acrylic polymer

Benzyl amine (available from BASF, Florham Park, New Jersey) 1.7% by wtwas mixed with 1.34% by wt of 1,6 Hexamethylene Diiscocyanate (availablefrom Bayer Material Science, Pittsburg, Pa., USA), in the presence of96.36% by wt of the low Tg polymer Joncryl 924 (Tg=−5° C.) availablefrom BASF Resins, Sturtevant, Wis., USA. The reaction was stirred for 5minutes.

(B) SCA in High Tg Acrylic Polymer

Benzyl amine (available from BASF, Florham Park, New Jersey) 1.7% by wtwas mixed with 1.34% by wt of 1,6 Hexamethylene Diiscocyanate, in thepresence of 96.36% by wt of the high Tg acrylic polymer (Tg=17.6° C.)from Procedure 1 (B). The reaction was stirred for 5 minutes.

Coating Compositions

Coating compositions were prepared according to Table 1.

TABLE 1 Coating Compositions (in weight part). Comp 1 Comp 2 Comp 3Example 1 Example 2 Low Tg Acrylic — — — — 18 polymer⁽¹⁾ Low Tg acrylic— — — — 45 polymer Joncryl 924⁽²⁾ High Tg Acrylic 63.0 (45) 63.0 63.063.0 (45) — polymer⁽³⁾ Polytrimethylene — 10.0 10.0 10.0 10.0 etherdiols⁽⁴⁾ SCA⁽⁵⁾ 1.36 — — 1.36 1.36 Fumed Silica⁽⁶⁾ — — 1.36 — —PPG2000⁽⁷⁾ 10.0 — — — — Bentone SD2⁽⁸⁾ — 1.36 — — — Tertiary butyl 5.05.0 5.0 5.0 5.0 acetate p- 14.0 14.0 14.0 14.0 14.0 Chlorobenzotri-fluoride 2-Ethyl Hexyl 0.8 0.8 0.8 0.8 0.8 Acetate Tint⁽⁹⁾ 80.6 80.680.6 80.6 80.6 Isocyanates 18.88 18.88 18.88 18.88 18.88 crosslinkingagent (Desmodur- N3330)⁽¹⁰⁾ Total 193.64 193.64 193.64 193.64 193.64⁽¹⁾Low Tg Acrylic polymer was from Procedure 1 (A). The amounts shown inparentheses represent the amount of the polymer used for preparing theSCA as described in Procedure 2. ⁽²⁾Low Tg acrylic Joncryl 924, Tg = −5°C., available from BASF Resins, Sturtevant, WI, USA. Joncryl 924 wasmixed with the SCA during the SCA synthesis as described in Procedure2(A). ⁽³⁾High Tg acrylic polymer was from Procedure 1 (B). The amountsshown in parentheses represent the amount of the polymer used forpreparing the SCA as described in Procedure 2(B). ⁽⁴⁾Polytrimethyleneether diols were prepared according to the process described in U.S.Pat. No. 6,875,514, col. 9, line 29 through col. 10, line 8.Characteristics of the polytrimethylene ether diols include: numberaverage molecular weight (Mn) was about 1,300-1,450, hydroxyl number of77.4-86.3 and a glass transition temperature (Tg) of about −75° C.⁽⁵⁾SCA (sag control agent) was produced according to the Procedure 2 inthe amount of polymer as shown in parentheses for Comparative 1 andExample 1. The amount of low Tg polymer Joncryl 924 used for SCAsynthesis for Example 2 is shown separately in the Table. ⁽⁶⁾FumedSilica: Fumed silica with hydrophobic surface treatment, sold asAerosil ® R-972 available from Evonik Degussa, Frankfurt, Germany, underrespective registered trademark. ⁽⁷⁾PPG2000: polypropylene glycol havinga molecular weight of 2000 from Aldrich Chemical Company, Product No.81380. ⁽⁸⁾Bentone ® SD2: organophilic clay, available from ElementisSpecialties, Inc., Hightstown, NJ, USA, under respective registeredtrademark. ⁽⁹⁾Tint: The tint used was 725P ™ which is a green Imron ®Tint available from E. I. DuPont de Nemours and Company, Wilmington, DE,USA, under respective trademark or registered trademark. ⁽¹⁰⁾Desmodur ®N3330: aliphatic polyisocyanate HDI trimer, available from BayerMaterialScience, Pittsburgh, PA, USA, under respective registeredtrademark.

Coating Properties

The coating compositions were applied on 4×12″ blasted steel panelsavailable from East Coast Steel Incorporated, Salina Rd,Sewell, N.J.,USA), using wet draw down forming a dry coating layer at about desiredthickness.

Tack free time of the coating layers was measured as described in“Testing Procedures”. Adhesion was measured using the aforementionedCross-Hatch adhesion test. A score of 0B indicates total failure onadhesion. A score of 5B indicates perfect adhesion.

Coating property data are shown in Table 2. The data indicated thatexamples of the coating composition of this disclosure, Examples 1 and 2had good adhesion to the steel panel substrates, improved gloss at 20°,good DOI, high wet coating thickness of 16 mils (about 406 microns), andhigh dry coating thickness of 7.2 mils (183 microns).

Comparative 1 failed to adhere to the substrate and had a long dry timeas measured by tack free time making it not suitable for practical use.The use of other rheology control agents, such as Benton or fumed silicaas described in Comparatives 2 and 3 failed to produce sag-free coatingwith wet coating thickness, also known as wet film thickness (wft),greater than 12 mils while maintain high gloss and DOI. Comparative 2had improved adhesion and shorter dry time, however, had a maximumsag-free wet coating thickness of 12 mils. Dry coating thickness forComparative 2 was below 6 mils. Comparative 2 also had low gloss and lowDOI. Comparative 3 had sag-free wet coating thickness of 8 mils, lowgloss and low DOI. Dry coating thickness for Comparative 3 was below 4mils.

TABLE 2 Coating Properties. Comp 1 Comp 2 Comp 3 Example 1 Example 2Adhesion to Steel 0B 4B 4B 5B 5B Panel Gloss at 20° 82.7 74.6 81.5 83.685.4 Sag-Free Wet 8 12 8 16 16 Coating Thickness (mils) Sag-Free DryFilm 3.6 5.4 3.6 7.2 7.2 Thickness (mils) DOI 83.82 53.04 74.69 82.0790.51 Tack Free Time 48 8 8 8 9 (hours)

1. A coating composition comprising a binder consisting essentially of:A) a crosslinkable component consisting essentially of at least oneacrylic polymer having one or more crosslinkable functional groups; B) apolytrimethylene ether diol having a Mn (number average molecularweight) in a range of from 500 to 10,000; C) a sag control agent; and D)a crosslinking component consisting essentially of at least onecrosslinking agent having one or more crosslinking functional groups. 2.The coating composition of claim 1, wherein the polytrimethylene etherdiol is polymerized from bio-derived 1,3-propanediol.
 3. The coatingcomposition of claim 1, wherein at least one of said one or morecrosslinkable functional groups is hydroxyl group, and wherein at leastone of said one or more crosslinking functional groups is isocyanategroup.
 4. The coating composition of claim 1, wherein the acrylicpolymer is a low Tg (Glass transition temperature) acrylic polymerhaving a weight average molecular weight of 5,000 to 100,000 and a Tg of−40° C. to 5° C.
 5. The coating composition of claim 1, wherein theacrylic polymer is a high Tg acrylic polymer having a weight averagemolecular weight of 5,000 to 100,000 and a Tg of 5° C. to 80° C.
 6. Thecoating composition of claim 1, wherein said sag control agent consistsessentially of a reaction product of an amine and an isocyanate.
 7. Thecoating composition of claim 6, wherein said isocyanate is selected from1,6-hexamethylene diisocyanate, 2,2,4-trimethylhexane-1,6-diisocyanate,2,4,4-trimethylhexane-1,6-diisocyanate, cyclohexyl-1,4-diisocyanate,isophoron diisocyanate, adduct isophoron diisocyanate, adduct ofhexamethylene diisocyanate, dicyclohexylmethane-4,4′-diisocyanate,xylylene diisocyanate, 1,3,5-trimethyl-2,4-bis(isocyanatomethyl)benzene,toluene diisocyanate, diphenylmethane-4,4′-diisocyanate, adduct oftoluene diisocyanate, or a combination thereof.
 8. The coatingcomposition of claim 6, wherein said amine is selected from benzylamine, ethylamine, n-propylamine, 2-propylamine, n-butylamine,2-butylamine, t-butylamine, n-pentylamine, α-methylbutylamine,α-ethylpropylamine, β-ethylbutylamine, hexylamine, octylamine,decylamine, stearylamine, cyclohexylamine, aniline, or a combinationthereof.
 9. The coating composition of claim 6, wherein said amine isbenzyl amine and said isocyanate is 1,6-hexamethylene diisocyanate. 10.The coating composition of claim 1 further comprising one or morepigments, one or more solvents, ultraviolet light stabilizers,ultraviolet light absorbers, antioxidants, hindered amine lightstabilizers, leveling agents, rheological agents, thickeners,antifoaming agents, wetting agents, catalysts, or a combination thereof.11. A substrate coated with the coating composition of claim 1, 2, 3, 4,5, 6, 7, 8, 9 or
 10. 12. A process for forming a sag-free coating layeron a substrate, said process consisting of the steps of: A) applying acoating composition over said substrate forming a sag-free wet coatinglayer having a wet coating thickness in a range of from 10 to 36 mils,wherein said coating composition comprises a binder consistingessentially of: i) a crosslinkable component consisting essentially ofat least one acrylic polymer having one or more crosslinkable functionalgroups; ii) a polytrimethylene ether diol having a Mn (number averagemolecular weight) in a range of from 500 to 10,000; iii) a sag controlagent; and iv) a crosslinking component consisting essentially of atleast one crosslinking agent having one or more crosslinking functionalgroups; and B) curing said sag-free wet coating layer to form saidsag-free coating layer.
 13. The process of claim 12, wherein saidsag-free wet coating layer has a wet coating thickness in a range offrom 12 to 36 mils.
 14. The process of claim 12, wherein said sag-freewet coating layer has a wet coating thickness in a range of from 16 to36 mils.
 15. A substrate coated by the process of claim 12, 13, or 14.